11.3 Nature of Municipal Solid Wastes 295
barrier against rainwater infiltration; it also
keeps out gas (and hence odors) and vermin.
(C) Working Landfill
- Daily cover
At the end of each working day, garbage is
covered with a 6–12 in. layer of soil. Daily
cover reduces odors, blowing litter, and helps
deter scavengers. - Garbage
In compliance with the requirement of most
authorities, as garbage arrives it is compacted
in layers within a small area known as a cell
to reduce the volume consumed within the
landfill. It helps to control odors, stop the
refuse from scattering and keeps off rats and
other vermin. Perhaps, the most precious
commodity and overriding problem in a land-
fill is air space. The amount of space is
directly related to the capacity and usable life
of the landfill. To increase the space, trash is
compacted into cells that contain only 1 day’s
trash (see Fig. 11.6). In one landfill, a cell is
approximately 50 ft long by 50 ft wide by
14 ft high (15.25 m × 15.25 m × 4.26 m). The
amount of trash within the cell is 2,500 ton
and is compressed at 1,500 lb per cubic yard
using heavy equipment (tractors, bulldozers,
rollers, and graders) that go over the mound
of trash several times. Once the cell is made,
it is covered with 6 in of soil and compacted
further. Cells are arranged in rows and layers
of adjoining cells known as lifts. As a further
way of conserving space, bulky materials,
such as carpets, mattresses, foam, and yard
waste, are excluded from most landfill.
(D) Leachate Collection System
Leachates consist of water which enter the land-
fill during rainfall or formed as a result of biologi-
cal activity within the landfill. As the water
percolates through the trash, it picks up contami-
nants (organic and inorganic chemicals, metals,
biological waste products of decomposition) and
is typically acidic. The function of the leachate
collection system is to control the flow of leachates
so that it can be properly removed from the land-
fill and treated.- Sand and gravel
A 12-inch layer of sand and/or gravel pro-
vides protection for a layer of thick plastic
mesh (called a geonet) which collects leachate
and allows it to drain by gravity to the leachate
collecting pipe system.
Fig. 11.8 A composite figure of a landfill showing a cell and
accompanying landfill activities (From Anonymous 2010j)
Note: (a) There are pipes for sampling the ground water around
the landfill for contamination from the landfill. (b) The bottom
of the landfill is slanted to facilitate the drainage of the leachates
to the pipes located at the bottom of the landfill. (c) The methane
(landfill gas) is being flared, although many modern landfills
have facilities for collecting the gas and using it for generating
electricity, for heating homes. (d) The ground water is slanting,
and some way from the bottom of the landfill